1. Field of the Invention
This invention relates generally to machines for processing plastic resin material prior to molding or extrusion, and specifically relates to gravimetric blenders. Gravimetric blenders are disclosed in U.S. Pat. Nos. 6,007,236; 6,188,936; 6,402,363; 6,467,943 and D424,587, the disclosures of all of which are incorporated herein by reference.
2. Description of the Prior Art
Many if not most gravimetric blenders operate with vacuum powered or other loaders that downwardly feed plastic resin material into one or more of the hoppers of the gravimetric blender, where the loaders typically are positioned on the top of the associated hoppers of the gravimetric blender. Vacuum loaders are disclosed in U.S. Pat. Nos. 6,089,794 and 7,066,689, the disclosures of both of which are incorporated herein by reference.
Older gravimetric blenders and many newer larger gravimetric blenders do not have removable hoppers; some small modern gravimetric blenders have removable hoppers. But even if removable, the hoppers cannot be removed if a vacuum loader is on top of the hopper, since the vacuum loader weighs a substantial amount, especially when filled with granular resin material.
Maguire Products, Inc. offers small capacity gravimetric blenders having removable hoppers. These small blenders with their necessarily smaller hoppers that are removable from the blender facilitate easy cleanout of the hopper by allowing removal of the hopper from the blender. A small gravimetric blender with a removable hopper is disclosed in U.S. Pat. No. 6,467,943.
If a gravimetric blender hopper has one or more loaders mounted on the hopper lid and the hopper is removable from the blender, presence of the loader(s) on the hopper lid limits, and in some cases may even eliminate, a worker's ability to remove the hopper from the gravimetric blender. A loader typically has a resin material feed line connected to it and is heavy. Vacuum loaders may weigh from 30 to 50 pounds each, making it awkward and sometimes dangerous for a worker to remove a loader from its position on the gravimetric blender hopper lid.
Moreover, the blender hopper top and hence the loader(s) are typically positioned high above the work floor, well beyond a worker's reach without using a ladder or a movable platform. This typical positioning of equipment in a plastic resin processing, molding or extrusion facility, cries for an easy way to move the loader(s) away from the hopper(s), in order to allow removal of the hopper(s) from the blender for cleaning and maintenance, without first having to remove the loader(s) from the hopper(s), by lifting the loader(s) off the hopper lid.
A previous approach to this problem has been to place a loader on a mount pivotally supported by a post, so that the loader can be swiveled out of the way by pivoting the mount around the post. Sometimes the post and mount are built with a cam or other apparatus so that a slight lift of the mount occurs on initial pivoting, to allow clearance for the loader when rotating sideways on the mount, out of the way of the hopper lid. The support post must be very substantial. The support post must additionally be fixed to a very substantial part of the gravimetric blender frame or fixed to the injection molding press or extruder to which the gravimetric blender is mounted, or even fixed to the facility floor, in order to support the loader.